Summary of work: Alzheimer's disease (AD) is the most widespread among several neurological degenerative diseases (dementias) that occur principally at later ages, occasionally before 60, but more frequently after age 70. This study examines prospective psychological, neurological, and neuropsychological changes in participants from the Baltimore Longitudinal Study of Aging (BLSA). Neurological and neuropsychological examinations are administered to participants aged 60 and older, repeating many of the tests that were administered to these subjects at earlier ages. Diagnoses of probable Alzheimer's disease follow the NINCDS-ADRDA criteria. In a recent publication, we showed that incidence rates of Alzheimer's disease from the Baltimore Longitudinal Study are consistent with published incidence rates despite its lack of representativeness. In this study, there were 1,236 participants (802 men, 434 women) with longitudinal follow-ups between January 1985 and May 1998. The average length of follow-up was 7.5 years, with participants evaluated every 2 years by physical, neurologic, and neuropsychological examinations. We diagnosed 155 cases of dementia and Alzheimer's disease based on criteria from the Diagnostic and Statistical Manual of Mental Disorders and National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association. Of the 155 cases of dementia, there were 114 (74%) cases of Alzheimer's disease. Incidence rates of Alzheimer's disease increased with age from an estimated 0.08% per year (95% CI 0.00 to 0.43) in the 60 to 65 age group to an estimated 6.48% per year (95% CI 5.01 to 8.38) in the 85+ age group for men and women combined. The doubling time of incidence rates was approximately 4.4 years. There was a trend for women to have higher incidence rates than men and for an association of fewer years of education with higher incidence rates; but these effects were not significant. The median time of conversion from mild cognitive impairment to diagnosis of Alzheimer's disease was 4.4 years. These results suggest that the incidence rates for Alzheimer's disease in the Baltimore Longitudinal Study are consistent with published rates in other studies.